I assume you're referring to PCIe slots and an x16 and x4 slot are the same size. If you put an x4 card into an x16 slot it should run fine, but only at x4 speeds, not x16 speeds because it is an x4 card.

4x and 16x are not the same size ( length wise ) but the connectors are . So a 4x card will fit in a 16x. Also it's good to note even if its a 16x its not always electorally 16x . Some slots if you look close you'll see its 1-8x based on the pins inside. You can also run a 4x card in a 1x slot if the back end is open ( kinda rare these day since they make them all just the large slots for convenes )

4x and 16x are not the same size ( length wise ) but the connectors are . So a 4x card will fit in a 16x. Also it's good to note even if its a 16x its not always electorally 16x . Some slots if you look close you'll see its 1-8x based on the pins inside. You can also run a 4x card in a 1x slot if the back end is open ( kinda rare these day since they make them all just the large slots for convenes )

You're right about the sizes! I've never seen a short x4 slot and I assumed it was identical to an x16 slot, but fewer pins. Looks like there are short x8 slots too. Live and learn (from other people who have a clue).